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Practical case: Half-wave voltage doubler

Half-wave voltage doubler prototype (Maker Style)

Level: Medium | Objective: Analyze and assemble a voltage doubler circuit to increase the peak voltage of an AC signal.

Objective and use case

In this practical case, you will build a half-wave voltage doubler (a basic Villard/Greinacher cascade) using two diodes and two capacitors. This circuit rectifies an AC input while simultaneously stepping up the voltage, yielding a DC output roughly twice the peak voltage of the AC source.

Why this circuit is useful in the real world:
* Generating high-voltage bias supplies for components like vacuum tubes, cathode ray tubes, or photomultipliers.
* Providing higher voltage rails for specific operational amplifier stages without requiring a custom, bulky step-up transformer.
* Powering low-current electrostatic devices, ionizers, or Geiger-Müller tubes.

Expected outcome:
* The input signal (V_in_AC) operates as a standard sinusoidal wave.
* The output voltage (V_out_DC) measures approximately 2 × Vpeak of the input signal, minus the forward voltage drops of the two diodes.
* Ripple voltage will be present on the DC output and will noticeably increase when a heavier load (lower resistance) is connected.

Target audience: Intermediate electronics students learning AC-to-DC conversion and fundamental multiplier topologies.

Materials

  • V1: 12 Vrms (approx 17 Vpeak) AC source, 50/60 Hz, function: main AC input signal
  • D1: 1N4007 rectifier diode, function: first clamping stage
  • D2: 1N4007 rectifier diode, function: second peak rectifier stage
  • C1: 100 µF / 50 V electrolytic capacitor, function: AC coupling and intermediate charge storage
  • C2: 100 µF / 50 V electrolytic capacitor, function: output smoothing and final charge storage
  • R1: 10 kΩ resistor, function: light output load to safely discharge capacitors after power off

Wiring guide

  • V1: connects between node NODE_AC and node 0 (GND).
  • C1: connects between node NODE_AC (negative terminal) and node NODE_MID (positive terminal).
  • D1: connects between node 0 (anode) and node NODE_MID (cathode).
  • D2: connects between node NODE_MID (anode) and node VOUT (cathode).
  • C2: connects between node VOUT (positive terminal) and node 0 (negative terminal).
  • R1: connects between node VOUT and node 0.

Conceptual block diagram

Conceptual block diagram — Half-Wave Voltage Doubler
Quick read: inputs → main block → output (actuator or measurement). This summarizes the ASCII schematic below.

Schematic

GND
                                                        |
                                                  [ D1: 1N4007 ]
                                                        |
                                                        v
GND --> [ V1: 12Vrms AC ] --(NODE_AC)--> [ C1: 100µF ] --(NODE_MID)--> [ D2: 1N4007 ] --(VOUT)--> [ R1: 10 kΩ ] --> GND
                                                                                            |
                                                                                            +---> [ C2: 100µF ] --> GND
Electrical Schematic

Measurements and tests

  1. Measure the AC Input Peak: Connect an oscilloscope or a multimeter (in AC mode) across node NODE_AC and node 0. A 12 Vrms input should read roughly 17 V peak.
  2. Measure the Intermediate DC Voltage: Place a multimeter (in DC mode) across C1. You should read approximately Vpeak – 0.7 V (around 16.3 VDC).
  3. Measure the Doubled Output (V_out_DC): Probe between VOUT and 0 in DC mode. The voltage should be approximately 2 × Vpeak – 1.4 V (around 32.6 VDC).
  4. Observe Output Ripple: Switch the oscilloscope to AC coupling and probe VOUT. You will observe a ripple wave matching the frequency of the input source (half-wave rectification).
  5. Test Load Dependency: Swap R1 for a 1 kΩ resistor. Notice how the output DC voltage sags and the ripple amplitude increases significantly, proving this topology is best suited for low-current applications.

SPICE netlist and simulation

Reference SPICE Netlist (ngspice) — excerptFull SPICE netlist (ngspice)

* Practical case: Half-wave voltage doubler
.width out=256

* Main AC Input Signal (12 Vrms -> ~16.97 Vpeak, 50 Hz)
V1 NODE_AC 0 SIN(0 16.97056 50)

* AC coupling and intermediate charge storage
* Connected with NODE_MID as positive and NODE_AC as negative terminal
C1 NODE_MID NODE_AC 100u

* First clamping stage rectifier diode
D1 0 NODE_MID 1N4007

* Second peak rectifier stage diode
D2 NODE_MID VOUT 1N4007

* Output smoothing and final charge storage
C2 VOUT 0 100u

* Light output load to safely discharge capacitors
* ... (truncated in public view) ...

Copy this content into a .cir file and run with ngspice.

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* Practical case: Half-wave voltage doubler
.width out=256

* Main AC Input Signal (12 Vrms -> ~16.97 Vpeak, 50 Hz)
V1 NODE_AC 0 SIN(0 16.97056 50)

* AC coupling and intermediate charge storage
* Connected with NODE_MID as positive and NODE_AC as negative terminal
C1 NODE_MID NODE_AC 100u

* First clamping stage rectifier diode
D1 0 NODE_MID 1N4007

* Second peak rectifier stage diode
D2 NODE_MID VOUT 1N4007

* Output smoothing and final charge storage
C2 VOUT 0 100u

* Light output load to safely discharge capacitors
R1 VOUT 0 10k

* Diode Model for 1N4007
.model 1N4007 D(IS=7.02767n RS=0.0341512 N=1.80803 EG=1.05743 XTI=5 BV=1000 IBV=5e-08 CJO=1e-11 VJ=0.7 M=0.5 FC=0.5 TT=1e-07)

* Simulation Directives
.print tran V(NODE_AC) V(VOUT) V(NODE_MID)
.tran 100u 500m
.op
.end
* --- GPT review (BOM/Wiring/SPICE) ---
* circuit_ok=true
* simulation_summary: The simulation shows the input AC voltage swinging between approximately -17V and +17V. The intermediate node (NODE_MID) is clamped and shifted, reaching a peak of about 32.6V. The output voltage (VOUT) successfully charges up to approximately 32V, which is nearly double the peak input voltage, confirming the voltage doubler operation.
* overall_comment: The SPICE netlist perfectly matches the BOM and wiring guide. The simulation results clearly demonstrate the expected behavior of a half-wave voltage doubler, with the output voltage reaching approximately twice the peak input voltage. This is an excellent didactic example.
* --------------------------------------

Simulation Results (Transient Analysis)

Simulation Results (Transient Analysis)

Analysis: The simulation shows the input AC voltage swinging between approximately -17V and +17V. The intermediate node (NODE_MID) is clamped and shifted, reaching a peak of about 32.6V. The output voltage (VOUT) successfully charges up to approximately 32V, which is nearly double the peak input voltage, confirming the voltage doubler operation.
Show raw data table (5027 rows)
Index   time            v(node_ac)      v(vout)         v(node_mid)
0	0.000000e+00	0.000000e+00	2.565925e-21	-1.89144e-18
1	1.000000e-06	5.331459e-03	5.419582e-10	5.331457e-03
2	2.000000e-06	1.066292e-02	1.097125e-09	1.066291e-02
3	4.000000e-06	2.132583e-02	2.236679e-09	2.132582e-02
4	8.000000e-06	4.265162e-02	4.716739e-09	4.265162e-02
5	1.600000e-05	8.530298e-02	1.109752e-08	8.530296e-02
6	2.994581e-05	1.596525e-01	3.640348e-08	1.596524e-01
7	4.360349e-05	2.324629e-01	1.285942e-07	2.324628e-01
8	5.923389e-05	3.157848e-01	6.926674e-07	3.157841e-01
9	7.569182e-05	4.035098e-01	4.463881e-06	4.035053e-01
10	9.313209e-05	4.964590e-01	3.310357e-05	4.964259e-01
11	1.114841e-04	5.942514e-01	2.714571e-04	5.939798e-01
12	1.306697e-04	6.964642e-01	2.279240e-03	6.941849e-01
13	1.507869e-04	8.036134e-01	1.447578e-02	7.891374e-01
14	1.727320e-04	9.204617e-01	5.134539e-02	8.691153e-01
15	1.929217e-04	1.027924e+00	1.015818e-01	9.263400e-01
16	2.144482e-04	1.142457e+00	1.586780e-01	9.837739e-01
17	2.454175e-04	1.307137e+00	2.410344e-01	1.066092e+00
18	2.845422e-04	1.515006e+00	3.449894e-01	1.169993e+00
19	3.627917e-04	1.930024e+00	5.525467e-01	1.377419e+00
20	4.627917e-04	2.458671e+00	8.169450e-01	1.641599e+00
21	5.627917e-04	2.984892e+00	1.080147e+00	1.904524e+00
22	6.627917e-04	3.508167e+00	1.341889e+00	2.165935e+00
23	7.627917e-04	4.027980e+00	1.601917e+00	2.425574e+00
... (5003 more rows) ...

Common mistakes and how to avoid them

  • Reversing diode polarity: Installing D1 or D2 backward will either clamp the voltage to a negative potential instead of positive, or block the charge from reaching the output entirely. Always check the silver band indicating the cathode.
  • Incorrect capacitor polarity: Electrolytic capacitors will fail or vent if reverse-biased. Ensure C1‘s positive terminal faces the diode junction (NODE_MID) and C2‘s positive terminal faces VOUT.
  • Using capacitors with low voltage ratings: C2 must handle the fully doubled voltage (2 × Vpeak). Using a 25 V capacitor for a 34 V output will cause immediate failure. Always select capacitors rated for at least 2.5 × Vpeak of the AC source.

Troubleshooting

  • Symptom: Output voltage is only equal to Vpeak (not doubled).
    • Cause: C1 is shorted, or D1 is open/damaged.
    • Fix: Verify D1‘s continuity using a multimeter diode test and check C1 for internal shorts.
  • Symptom: Output voltage (VOUT) is zero or close to zero.
    • Cause: D2 is installed backwards (blocking the DC flow), or the load resistor R1 is completely shorted/too small, collapsing the multiplier’s charge.
    • Fix: Verify D2 orientation and ensure R1 is at least 10 kΩ for testing.
  • Symptom: Loud pop or bulging capacitor upon power-up.
    • Cause: C2 voltage rating was exceeded or it was connected with reversed polarity.
    • Fix: Immediately disconnect power. Replace the damaged capacitor, double-checking correct polarity and a safe voltage rating (e.g., ≥ 50 V).

Possible improvements and extensions

  • Add multiplier stages: Cascade additional diodes and capacitors to turn this circuit into a Cockcroft-Walton voltage tripler or quadrupler for even higher DC potentials.
  • Build a full-wave voltage doubler: Reconfigure the circuit into a full-wave doubler topology to double the ripple frequency, which reduces the required size of the filter capacitors to maintain a stable output under load.

More Practical Cases on Prometeo.blog

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Quick Quiz

Question 1: What type of circuit is being built in this practical case?




Question 2: What are the primary components required to build this voltage doubler?




Question 3: What is the expected DC output voltage of this circuit?




Question 4: Which of the following is a real-world application for a voltage doubler?




Question 5: What happens to the theoretical output voltage due to the diodes in the circuit?




Question 6: How does a heavier load (lower resistance) affect the DC output?




Question 7: What type of input signal is used in this practical case?




Question 8: Why might a voltage doubler be preferred over a step-up transformer for certain op-amp stages?




Question 9: Which specific cascade topology is mentioned as the basis for this half-wave voltage doubler?




Question 10: What type of devices are suitable to be powered by this circuit due to its low-current characteristics?




Carlos Núñez Zorrilla
Carlos Núñez Zorrilla
Electronics & Computer Engineer

Telecommunications Electronics Engineer and Computer Engineer (official degrees in Spain).

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