ATtiny85 and high frequency PWM for driving a ferrite transformer
In an ATtinyXX there are two timers. Timer0 can be clocked at the same CPU frequency, by setting the corresponding bits (see below) in the TCCR0B (for timer 0).

At 8 MHz and 8 bit, the PWM will have a frequency of \$\frac{8\ MHz}{2^8} = 31.25\ kHz\$.

Timer 1, instead, can be also clocked by the PLL (up to 64 MHz), which multiplies the internal frequency by 8, yielding a maximum frequency of \$\frac{64\ MHz}{2^8}= 250\ kHz\$.

Here's the timer 0 control register B:



And here's the CS0x setting table:



Here's the timer 1 control register:



There you must set the correct clock prescaler value according to the table:



To enable PLL you must set bits PCKE and PLLE in PLLCSR.