Following diagram (Fig. 1) shows my PWM (Pulse Width Modulation) speed controller. This is fed from LGB power pack set at about maximum voltage. This design is my favorite and utilised many times in my projects.
IC2A and IC2B consist a free running triangle wave generator. The frequency is determined by C3. I did not want to hear switching noise. So I set the frequency about 10KHz with C3 of 550pF. This is still not above audible frequency, but quite negligible and I can not hear any noise. Using higher frequncy has other reason mentioned later. The frequency changes inverse proportional to the value of C3. That means if you make C3 as 5.5nF then you will get 1KHz. High frequency than 10KHz was not possible because of limitation of performance of the operational amplifier IC2.
The selection of chopping frequency affects the train operation. With 10KHz the output current is so smooth and does not give any kick to the motor in low speed and low speed operation is not so good. To have good low speed operation I recommend to choose 50 to 100Hz chopping frequency. If operational amplifiers with poorer voltage swing range (like 741 type) used, value of R4 needs to be smaller than 22K.
The controller handle is mounted directly to the shaft of potentiometer "POT2" and only 90deg out of 270 deg full stroke is used. "POT1" is provided to adjust span of the control.

IC2AとIC2Bは三角波発生回路を構成しFig. 2の”A"のような波形を出力します。キーンとゆうようなスイッチングノイズがいやだったのと後述の理由で、周波数は約10KHZとしています(C3:550pF)。可聴周波数内ですがまったく音は聞こえません。周波数はC3の値に反比例します。使ったオペアンプの能力からして10KHZが限界でした。出力電圧幅の狭いオペアンプ(741クラスとか)を使うとR4をもっと小さい値にしないと発振しません。
制御ハンドルはPOT2に直接取り付け、POT2の回転角の約90度ぐらいを使っています。 POT1でコントローラーハンドルのスパンを調整します。

Fig.1 Circuit Diagram

Waveforms of each part are shown in Fig. 2. The triangle waveform at "A" is compared with the voltage ("B") set by the controller handle. If the B>A the output of IC2C goes high and turns on MOSFET Q1. By changing the voltage level at "B", "ON" period of Q1 changes. Thus the average output voltage changes according to the voltage level "B".


Fig. 2 Waveforms

I wanted to have smoke generator on my Stainz even in slow speed. So I modified the circuit of Stainz as Fig. 3. Combined with above PWM controller, the capacitors in the circuit are "peak charged" to give full voltage to the smoke generator and lamps. For this purpose higher chopping frequency better to reduce required capacitance. WIth this circuit the smoke generator of my Stainz starts smoking even the motor still does not start. Actually the operation of the smoke generator seemed too vigorous, I need to reduce the master power pack voltage. One drawback of the circuit is both head and tail lamps are ON in low speed because of inductance of the motor. I have an idea to overcome this, but not tested yet.

Stainzの発煙装置が通常使用速度ではまったく機能しないので上記のPWMパワーパックとのくみあわせで、Fig. 3のような回路を組み込みました。整流器とコンデンサの働きで、発煙装置とランプには速度にかかわりなくほぼフル電圧が供給されます。事実私のStainzは動き出す前から煙を吐き出します。でもちょっと電圧が高すぎるみたいなので、現在はマスターのLGBのパワーパックの出力をすこし絞っています。チョッピング周波数は高いほうがコンデンサの容量を節約できますので、10KHzに設定しています。欠点は低速ではヘッドランプとテールランプが同時についてしまいます。これはモーターのリアクタンスの影響なのでこの回路では解決不能です。解決法は考えてあるのですがまだ試していません。

Fig. 3 Loco Circuit

Installation of the controller. Zeroing of the control lever is simply done by turning the potentiometer base.
If I make next one I will use micro controller instead.



inserted by FC2 system