This piece of Open-Source software can be used to simulate transformer power supplies and to select components for that.

The software is written in Lazarus Pascal. The two versions differ. The version 2

- corrects an error in the simulation of double-coil transformers with two-diode-rectifier (version 1 yielded too small voltages),
- estimates the diode voltages with a log function and not linearly like version 1 (yields higher voltages),
- changes the input fields: during editing the fields are marked green, while during entry no simulation takes place, after pushing the enter key the entry is checked and simulated, parameters that are changed by the program appear in yellow, errors in entries are marked red.

Version | Windows | Linux | ||
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Source code | Executable | Source code | Executable | |

2 | V2 Win Source | V2 Win64 Executable | (not provided) | |

1 | V1 Win Source | V1 Win64 Executable | V1 Lin Source | V1 Lin Executable |

- Selecting type
- Transformer properties
- Diodes and rectifier bridges
- Capacitor, DC current
- Simulation
- Results

Rectification with one single diode, one transformer coil, half wave rectification | |

Rectification with a rectifier bridge of the Graetz type with four diodes, a single transformer coil, full wave rectification | |

Rectification with two transformer coils and two diodes, full wave rectification |

In half wave rectification only the positive halfwave is active, the duration over which the capacitor is loaded is shorter, the duration over which the consumed DC current has to be supplied from the capacitor alone is longer.

When using a two coil transformer with two diodes both half waves are actively loading the capacitor. As only one diode with its conducting state voltage drop is required, the voltages are at their maximum.

Top of page | Type | Transformer | Diodes | Capacitor | Simulation | Results |
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The other parameters are optional, but are required for a realistic modelling. The transformer coil(s) consist of a wire with a resistance (Ohm's law). The coil resistance in Ω can be measured on the transformer. To account for the voltage losses over this inner resistance Ri the transformer is designed for a higher voltage. This is called the no load voltage, V. Only if the design current flows the nominal voltage is reached, the over voltage is consumed by the inner resistance of the coil(s).

Some transformer sellers publish the no load voltage or the no load voltage factor, U

An additional effect that occurs in rectification is that all voltages are effective values U

Rectifying this voltage with a diode and loading a capacitor with that yields approximately 12 V and not 9 V!

Additionally considering the compensation of the inner resistance yields even higher voltages following rectification (no load):

The maximum voltage of the 9 V transformer now is higher than 17 V. A 16 V capacitor would be overcharged with that. This effect is even more dramatic with very small transformers with less than 1 VA.

If you change the power of the transformer in the software, the no load voltage factor is estimated from the size of the transformer and changes occur in the factor and in the no load voltage. If the nominal current (in mA) is changed the transformer power and the other parameters are changed, too. So better first select nominal current and/or power first, no load voltage, no load voltage factor and coil resistance later on. With double coil transformers the parameters voltage, current and inner resistance apply for one coil each, except for the power of the transformer.

Top of page | Type | Transformer | Diodes | Capacitor | Simulation | Results |
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In version 2 of the software a logarithmic function is used to calculöate the current-depending forward voltage.

Caused by the high inner resistance of the transformer the capacitor is charged slowly and reaches saturation only after several hundred half waves. If a microcontroller needs a high slew rate of the operating voltage then a large capacitor is not a good idea.

The consumed current in mA is written to the next edit field. If this current nears the nominal current of the transformer the voltage on the load capacitor drops and the ribble increases, like here.

Switching between 50 and 60 Hz frequency can be done in the respective selection field. It changes the times of the displayed waves.

Top of page | Type | Transformer | Diodes | Capacitor | Simulation | Results |
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Top of page | Type | Transformer | Diodes | Capacitor | Simulation | Results |
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