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| − | + | PWM a.k.a. pulse-width modulation is a voltage waveform usually seen in power electronics such as motor drives and power supplies. | |
| − | PWM a.k.a. pulse-width modulation is a voltage waveform usually seen in power electronics such as motor drives and power supplies | + | |
| − | The main idea in PWM is to switch voltage either fully | + | The main idea in PWM is to switch voltage either fully on or off so rapidly that output device "feels" only the average voltage caused by pulsed voltage. |
==Duty cycle== | ==Duty cycle== | ||
| − | Duty cycle describes the ratio of pulse on/off timing | + | Duty cycle describes the ratio of pulse on/off timing. |
| − | I.e. if duty cycle is 10%, then the PWM signal is "on" for 10% of time and "off" for 90% of time. I.e. if "on" equals voltage of 48VDC and "off" 0VDC, then 10% duty cycle equals effective voltage of 4.8VDC | + | I.e. if duty cycle is 10%, then the PWM signal is "on" for 10% of time and "off" for 90% of time. I.e. if "on" equals voltage of 48VDC and "off" 0VDC, then 10% duty cycle equals effective voltage of 4.8VDC. |
| − | + | ==Pros and cons in power applications== | |
| − | == | + | ===Pros=== |
| − | + | * Very high efficiency due to low losses in electronics | |
| − | + | * Usually very little heat sinking needed | |
| − | + | * Easy to produce in digital circuits | |
| + | * Robust | ||
| + | ===Cons=== | ||
| + | * Increased [[Electromagnetic interference|EMI noise]] compared to linear voltage | ||
==Usage in GD products== | ==Usage in GD products== | ||
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Inductance of motor coils will average the PWM pulses to equivalent DC. If motor inductance is very low, additional inductor is needed between drive and motor phases. | Inductance of motor coils will average the PWM pulses to equivalent DC. If motor inductance is very low, additional inductor is needed between drive and motor phases. | ||
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| − | Compared to analog input in VSD products 0% PWM duty cycle equals -10V, 50% equals 0V and 100% equals +10V. Benefits of using PWM instead of analog | + | ===As reference signal=== |
| + | In some drive models, PWM signal can be used also as reference signal to replace analog signal (the +/- 10V control). In this case PWM voltage is typically 3-5V and the duty cycle of signal determines the amplitude. | ||
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| + | Compared to analog input in VSD products 0% PWM duty cycle equals -10V, 50% equals 0V and 100% equals +10V. Benefits of using PWM instead of analog reference: | ||
* [[Electromagnetic interference|EMI noise]] tolerant | * [[Electromagnetic interference|EMI noise]] tolerant | ||
* Easy to galvanically isolate | * Easy to galvanically isolate | ||
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==Links== | ==Links== | ||
[http://en.wikipedia.org/wiki/Pulse-width_modulation Wikipedia PWM article] | [http://en.wikipedia.org/wiki/Pulse-width_modulation Wikipedia PWM article] | ||
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