Now transistors are widely used in pulse devices of radio engineering, carrying out thus a role of an electronic key. Therefore calculation of the transistor is one of paramount tasks at design of pulse devices.It is required to you
- reference book on transistors bipolar to low-frequency average and big power;
- basic data for calculation;
- methodical recommendations with formulas for calculation of the transistor.
Calculate dynamic losses of the transistor. This indicator includes the size of losses at inclusion, and also switching off of the transistor. Dynamic losses arise because between the emitter of Special design bureau and the collector is the small capacity which interferes with instant transition of the transistor from one state in another and holds it in linear situation.
Calculate the power consumed from a power source on a formula: Rvkh = Rvykh/?, in which Rvykh – an indicator of the power transferred to loading, and? – Stabilizer efficiency. Carrying out calculations, pay attention to that fact that good converters have efficiency of 95-97%.
Having used the reference book on bipolar transistors, determine the maximum output tension. Remember that in obratnokhodovy converters tension indicator on a collector will be above a supply voltage indicator. So for determination of the maximum tension on a collector increase an indicator of the maximum tension of amplitude network food by two.
Calculate static losses. They will be equal to integral of work of effective current and tension of falling on the transistor.
Determine a resistor resistance indicator by a formula: Rst = Ike (eff) *ukenas, considering tension of management, strengthening coefficient, and also size of effective current.
Calculate dynamic losses, considering that fact that the speed of closing and opening of the transistor is limited to collector capacity. Tension on a collector generates current in base: its orientation is opposite to current of management so it interferes with possibility of instant switching of the transistor from one state in another.
Find time of switching off of the transistor on a formula: t (vykl) = U*C/I. In other words, this formula allows to determine the speed of closing of the transistor provided that current through the capacity of a collector supports the transistor in the carrying-out state.
Determine the maximum permissible temperature of heating of the case of the transistor. Make calculation for a formula: Tkr = Tsr+rsumm * (Rt (Krk) +Rt (is glad-sr) to +Rt (to - it is glad)) where Tsr – an indicator of ambient temperature, Rsumm – the total power of the transistor, Rt (is glad-sr) - thermal resistance a radiator air, Rt (Krk) – thermal resistance a crystal case of the transistor and Rt (to - is glad) - thermal resistance the case radiator.